This invention relates to measuring and testing, and more particularly to an improved method for optically determining the stress-optical constants of optically isotropic and anisotropic materials.
Knowledge of the stress-optical constant or coefficient is useful when designing products manufactured from optically isotropic and anisotropic materials to prevent product failures when the material in the product is stressed. For a cracked specimen, the stress distribution at the tip of the crack is responsible for the propagation of the crack under certain conditions, and ultimately may result in a fracture of the product.
Prior art methods for measuring stress-optical constants of optically isotropic and anisotropic materials involve the use of a type of interferometer for producing an interferogram in a stressed specimen. For accuracy, it is necessary for the interferometer and the load on the specimen to be accurately calibrated. This requires very delicate and very expensive instruments. The instruments must be operated by specialized scientific personnel, further increasing the cost of these measurements. As a consequence, stress-optical constants generally are not measured or provided to the designer by the manufacturer of the material among the other standard mechanical specifications for the material.